Hey Sophist, explain the whole "older parts of the universe" thing to me. Isn't it all the same age?
Yes and no. The current universal theory is the Big Bang explosion, or that all matter originated at once and expanded in all directions, creating our known universe. We discovered that the universe has an end, but is still expanding, and has a beginning, but no center origin point. We learned this by two discoveries: the cosmic microwave background radiation and the Red Shift. As visible light expands, it's frequency lowers and it shifts into the ultraviolet spectrum. So, by building equipment that can see this UV light, we can tell, in simple terms, that the universe is constantly expanding in all directions, by observing the very far away light as it has shifted into another spectrum.
It's kind of wrong to say that any point of the universe is older (theoretically we're all older than the very edge that has been expanding since the Big Bang completely ended), but it's theorized that a good part of the universe was already settling as edges were still cooling from the expansion. Imagine a balloon expanding in all directions, the air in the center would be 'more still' than the air pushing against the fabric. We're kind of on the later side of the cool down instead of the earlier, meaning some part of the universe is very slightly older than the Milky Way Galaxy, and has certainly existed before the MW existed at all. Therefore, stars could have gone through nova collapse before our galaxy took spiral shape. It's more of that planets have existed before WE did, rather than the whole universe being of completely varying age.
This is a good example of explaining why this is. This is just a diagram rather than an actuality, as that dark expansion encompasses the entire universe, as it expands in every direction. ( e see the 'edge' of the universe by observing the cosmic background radiation, or the radiation still emanating from the Big Bang, and it is getting further and further away from us, in all directions.) Development of planets and galaxies took a long time, but some came first and others later. As the universe was very hot still, it was just a swirling mass of elements, before they all began pulling on one another with gravity. The Milky Way was a later development of a galaxy, therefore, theoretically, life could have existed on earlier planets.
Is this proven across the universe, or are these sets of circumstances simply being extrapolated from our knowledge of our own galaxy? How much do we know about the other galaxies, and if these same rules are certain to apply to them too?
This is an honest question, not a devil's-advocate one.
Unless all the stars in the universe suddenly change, yes, this is proven across the universe. As light from stars anywhere in the universe reach us, we have equipment that can register what elements are burning in these stars. The equipment is sensitive enough to detect the elements in any star it can see without extreme exposure, such as the
deep space field. We can tell elements in stars outside our galaxy, and very far off, and they have all been uniformly the same. It's just the way stars are naturally, some are very large and have been burning for a long time, meaning there are more elements inside them. We know surprisingly a lot about other galaxies. Once you leave the atmosphere of Earth, and with a precision camera and exposure instrument, you can see basically anything in light, including other galaxies. We can tell roughly how many stars are in them, how old they are in relation to us, and much more. Take a peek through the
Wiki page on the Andromeda galaxy, our closest spiral galaxy (that will eventually crash into the Milky Way and kill us all).